I'm debating whether to sell mine. I saw the one that went on eBay, and mine is superior. It was originally purchased on 5/6/2006, so it's one of the last new ones sold, it's still sealed (box was never opened) and is the best equipped 12" ever sold - with 100gb HDD. And best of all, I found that it has valid AppleCare until 5/2009 and I had it transferred to me. I think it'd be in demand more from collectors or fans of 12" PBs than from those looking for just another inexpensive computer. For those I'd recommend used PBs or MacBooks. Maybe I should hold onto it for 10 more years to see if 12" attain collectible status!
Maybe in 10 years there could be a collector that would want one but from what I noticed from apple collectors, they actually like to take it out to use it.. so meaning most collectors probably already own one and is currently playing with one.
I think its a waste of the original $1799 + apple care to just leave it in the box. I'd say either sell it or keep it and use it. For one in a sealed box I bet you can get about $950-$1000 on ebay. Especially if its still under applecare. I'd say just try to sell it before apple care is closer to expiration. You can use that $950 towards a nice mbp or a macbook.
One reason that I didnt buy the 12" is because everyone that I know always ends up with a logic board failure or issue from the 12" whether it be the 1.33Ghz or the 1.5Ghz. I know currently 6 people with 12" powerbooks and 4 of the 1.33ghz logic boards died and the other 2 with the 1.5Ghz logic board issues.
Especially even spending $600 and if the logic board dies within 6-12 months with no apple care is a $600 down the drain. Also you dont know if that 12" powerbook that you bought from the person on ebay was the original owner or if he had a logic board replace or anything else serviced. From what I noticed from the powerbooks is that once a logic board gets replace I usually see another one needed within 6 months. I guess its a risk like everything else though.
One other reason that kept me from buying one is that I think Steve Jobs will introduce something to replace the 12". It might not be this year or next year but sometime after that. Or the macbook air will get a complete redesign..I think that the macbook air will be worth of the replacement for the 12" powerbook in the next revision. Then I think we'll see a massive price drop for the current 12" powerbooks and people trying to sell one to make clear for the new macbook air purchase.
I think it isnt coincidence too that the mba is the same price as what the 12" powerbooks were. And I owned 2 mba's before the $1799 model.. man that was a sweet little machine, when the screen closed it looked like the 12" powerbook but squashed and smaller and carrying it around was awesome. I cant wait to see what the revisions are and what they will do to the mba to separate it to the aluminum macbooks.
Not to mention that the mba is already 3.5x faster than the 12" powerbooks, gorgeous led screen and when ssd drives get cheaper.. its like having a 10,000rpm raptor drive (I tested the ssd 64gb version to the raptor drive on my mac pro and it was pretty much a dead tie or raptor drive was 1 sec. faster from reopening due to cache though) with a much faster seek time in an ultraportable laptop. =D